Retardation-coil system



April 8, 1930. H. WHITTLE 1,753,325

RETARDATION COIL SYSTEM I Filed Jan. 28, 1928 ATTORNEY Patented Apr. 8,1930 vireo STATES PATENT OFFICE HORACE WHITTLE, or MAPLEWOOD, NewJERSEY, ASSIGNOR T0 BELLTELEPHONE LABORATORIES, INCORPORATE on NEW YORK,N. Y., A CORPORATION OF NEW YORK RETARDATION-C IL SYSTEM Applicationfiled January 28, 1928. Serial No. 250,163.

This invention relates to composite sets used in conjunction withsuperposing direct current signaling channels and telephone channelsupon the same line circuits and especially to retardation coils used inconjunction with composite sets applied to phantom circuits. p

In order to utilize the ordinary telephone circuit for the doublepurpose of speech transmission and transmission of direct currentsignals, such as telegraph or supervisory signals, it is necessary toprovide some means at the terminals for separating the signals anddirecting them into their respective channels. A condenser is usuallyprovided which excludes the direct current signals from the telephonerepeating coils, while a coil of high impedance, or retardation coil isprovided to prevent the passage of voice currents to the direct currentsignaling instruments.

Also to prevent cross fire, that is, one direct current instrumentresponding when a signal is being received by another, it is essentialthat there be no mutual inductance between the retardation coils. At thesame time it is requisite that the inductance of the coils which areassociated with each side of the telephone line be always balanced orequal; otherwise when two such telephone lines are used in aphantom'circuit cross talk from the phantom to the side circuits wouldresult.

The method of accomplishing the above result which is described in thecopending application of Messrs. E. L. Schwartz and J. Williams, SerialNo. 230,219, consists in providing two cores on which one-half of eachretardation "coil is placed poled in such a manner that there is nomutual coupling, while at the same time the inductance balance betweenthe coils is maintained.

Whereas in'the prior art the balancing has been confined to theindividual side circuits it has been found that an unbalance between thebranches of the phantom circuit is still possible. For instance, i'fonly'oneof the direct current circuits were in operation the retardationcoils in one side circuit would have a dliferent lmpedance from those inthe other resulting in noise in the phantom circuit if both sidecircuits were exposed to some external voltage along the line.

Heretofore' unbalancing' of the phantom circuits was maintained withincertain specified limits by the use of stable cores, thereby involvingconsiderable expense.

Oneobject of this invention therefore, is to maintain the impedance ofthe side circuits which'form the branches of a phantom circuit balanced,when any or all of the direct current signaling circuits which areassociated therewith are in operation. Another object of the inventionis to prevent noise currents from being induced in the phantom circuitas a result of external electric disturbances which might be inproximity to the lines somewhere along their length.

A feature of the invention resides in placing a portion of each c'oilon'each of four cores and poling them in sucha manner that a ages in anyof the other coils.

Another feature of this invention resides in the use of. cheaper coressince therequirement of core stability isabolished by virtue of all theretardation coils having balanced impedances when dilferent currents areflowing in the direct-current signaling circuits.

A better understanding of the invention may be had by reading thefollowing de-' scription together with the accompanying drawing, theSingle figure of' which shows a is shown for the sake of: simplicity."The phantom circuit may be of any well known current through one coilwill not induce volttively to a winding of the repeating coils 13 and 23by means of which the speech actuwindings 51, 52,

ated elements are associated with the line.

'hese circuits together with their associated lines are hereafterdesignated side circuits. As is customary in phantom circuits, leads areprovided connecting the mid points of the side circuit repeating coilwinding which are adjacent the lines to a winding of the phantomrepeating coil 16. These connections must always be maintained at theelec trical mid point of the coil for the proper operation of thephantom circuit. The other winding of the phantom repeating coilterminates in a speech actuated element similar to those associated withthe side circuits. The speech actuated elements are not herein shown butmay be a telephone transmitter and receiver of any well known design, ora telephone repeater as is customarily used for amplification purposes.

The composite set comprises the retardation coil systems 30 and whichare physical identical although serving difi'erent purposes. as will behereafter described.

A Morse telegraph transmitting and receiving set is associated with eachline wire of the side circuits through a coil of the retardat on-coilsystem 30. In order to direct telegraph signals and speech signals intotheir respective circuits, condensers 14 and 15 and 24 and 25 incircuits 10 and 20 are provided which exclude the direct currenttelegraph signals from the telephone repeating coils 13 and 23. Thespeech s gnals are in turn excluded from the telegraph sets 31, 32, 33and 34 by means of a shunt path comprising the retardation coils whichhave high impedance to voice frequencies.

The shunt path for the side circuit 10 may be traced from the line wire11 through the retardation coil w ndings 39, 40, 41 and 42, condensers35 and 36 in series, the retardation coil windings 43. 44. 45 and 46 inthe order named, back to the line wire 12. The shunt path for the sidecircuit 20 may be traced from the line 21 throughthe retardation col-windings 47, 48, 49 and 50 in series, condensers 37 and 38, theretardation coil 53 and 54 in the order named, to the line wire 22.These coils eliectively block the passage of currents of speechfrequencies, but have no effect on the direct current signals passingthrough to the telegraph instruments.

. The retardation coil connected to each line wire comprises fourwindings in series, all

of which have the same number of turns and are similar in all respects.All the coils have one of their windings on each of the four magneticcores 55, 56, 57 and 58. Thus the telegraph set 31 is connected to oneside of the side circuit 10 through the coil which comprises the fourwindings 39, 40, 41 and 42 which are disposed respectively on cores 55,56, 57 and 58. Similarly the connections of the other telegraph sets 32,33 and 34 may be traced to the line wires 12, 21 and 22 of the sidecircuits 10 and 20 through their associated coils.

Since all the coils have a winding on each of the cores resulting in acommon magnetic path therefor, it follows that any change in theinductance of one of the coils will be accompanied by a similar changeof inductance in all the others. At the same time, however, that theinductance of the coils are maintained balanced there must be no mu tualcoupling between any of the coils, since should any be present, crossfiring, or one telegraph instrument responding when a mes sage is beingtransmitted to another, would result.

The mutual coupling between the coils is made zero or at least at avalue, which for all practical purposes may be neglected, by the mannerin which the windings which comprise the coils are poled on the cores orin the circuit.

As an example of one possible arrangement let it be assumed that thewindings as shown are all wound in the same direction on theirrespective cores, starting from the same end.

If a direct current signal is being transmitted to the Morse set 31, itspath maybe traced thereto from the line wire 11, through the corewindings 39, 40, 41 and 42 in the direction or" the arrows- As thiscurrent builds up, a flux is established in the cores 55, 56, 57 and 58which induces voltages in the other windings placed thereon in adirection opposite to the current, and since all the windings are woundupon the cores in the same direc tion, the induced voltages willlikewise be in the same direction. But in order that these inducedvoltages have no eniect upon the telegraph instrument associated withthe. respective coils, it is necessary that the windings of each coil bepoled so that the resultant coil voltage is Zero. Thus, in the coilcomprising windings 43, 44, 45 and 46, two windings 43 and 44 are poledin one direction, whereas windings 45 and 46 are oppositely poled.Likewise, the coils associated with sets 33 and 34 must also have twowindings poled in the same direction and two in the opposite directionto those in the coils associated with set 31. Arranged in this manner itmay readily be observed that when-the set 31 is in oper ation, thevoltages induced in two windings of each of the other coils will balanceand annul those induced in the other two windings of the same coil,thereby leaving the telestood that the invention is. not to be limitedvto those skilled in the art within the scope of thisinvention; the'onlyrequisite being that with respect to'the windings of each specific coil,the other coils must have two windings similarly poled and twooppositelypoled.

Further limitations for the successful operation of the invention arethat the cores 55, 56, 57 and 58 must be similar and the wind ingsthereof must have the same number of turns and be exactly alike in allother respects.

Almost any type of core may be successfully employed, the arrangement ofwindings to be used being dictated by ease and economy in manufacture.For instance, a toroidal core could be used having all the windings inone direction, the proper poling effect being obtained by the manner inwhich the windings are connected in the circuit. A shell type core couldbe used having its winding concentrically wound upon the center leg.

l/Vhenever any of the Morse circuits are in operation the condenser forexcluding the direct current signal from the repeating coil and which isassociated with the circuit being used is intermittently charged at alow frequency of the order of, say, 20 cycles due to these telegraphsignals. If this frequency were allowed to pass to the telephonerepeating coil harmonics thereof would be generated in the coil,resulting in what is known as Morse thump, which would be audible in thetelephone receivers. To prevent this a path to ground is provided fromeach of the lines 11, 12, 21 and 22 at a point between the abovementioned condensers and the repeating coils 13 or 23, as the case maybe. The path to ground from line wire 11 may be traced through condenser61 and the windings 68, 64, 65 and 66 of the retardation coil, while thepath from line wire 12 is traced through condenser 62 and the windings67, 68, 69 and 70, which comprise a second retardation coil. These tworetardation coils are connected together and grounded at the point 71.Corresponding circuits are provided for lines 2]. and 22. These pathsreadily drain the condensers 14, 15, 24 and 25 of charges resulting fromthe operation of the Morse circuits. The four retardation coils thusprovided comprise a system similar in all respects to that used forseparating the voice frequencies from the telegraph transmitting andreceiv-I ing sets. If any or all of the Morse legs are in operation thedraining of these condensers through the respective retardation coilsdoes not disturb the balance'of the phantom circuit, as will readily beappreciated from the description of the operation of the coil systemalready described.

As the inductance-of the retardation coils of both side circuits arebalanced under all conditions, it follows that not only will theimpedance of bothsides, of the side circuits be balanced for allfrequencies traversing the side circuits, but also both sides of thephantom circuit will'present the same impedance to currents of differentfrequencies transmitted over the phantom circuit. Thus, the possibilityof cross talk from the phantom to the side circuits due to unbalance inthese coils is effectively prevented.

The necessity of using expensive stable cores to maintain the unbalanceof the phantom circuit within certain prescribed limits is also obviatedsince by theinvention both sides of the phantom are inherently balanced.

Although the invention has been described with respect toa specificembodiment thereof, it may be used in any part of thephantom circuitwherever the desirabilityof separating the voice from a direct currentsignal ispresented. It is understood that theinventi'on is to be limitedonly by the scope of the appended claims. a I i What is claimed is: I

1. In a phantomed telephone system, a pair of side circuits, means forsimultaneously superposing alternating current signals and directcurrent signals on said circuits, and means to aid in separating saidsignals comprising a retardation coil associated with each'line wire ofeach side circuit, said retardation coils each having portions of theirwindings disposed on a plurality of common cores to produce the samefluX linkage for changes of current in any of saidcoils, the windings oncertain of said cores being reversed to neutralize inductive couplingbet-ween the coils.

2. In a phantomed telephone system, a pair of side circuits, adapted forthe simultaneous transmission of alternating current signals and directcurrent signals, separate terminal apparatus responsive tosaidalternating; current signals and said direct current signals, mean toaid in directing said signals into their respective terminal apparatus,said means comprising a retardation coil connected to each line wire ofeach side circuit, a plurality of cores commonto said coils,

"said cores having windings from each coil disposed on them, certain ofsaid windings being reversed to neutralize the lnductlve coupling ofsaid coils.

3. In a phantomedtelephone system apair of side circuits havingtermi-nalapparatus associated therewith, means for simultaneouslysuperposingalternating current signals and direct current signals uponsaidcircuits, and means to aid in directing said signals into theirrespective terminal apparatus, said means comprising four retardationcoils and four cores, said coils each comprising four windings, each oneof said windings being disposed on one of said cores and poled in such amanner that there is negligible coupling between anyof the coils.

4. In a signaling system adapted for the simultaneous transmission oftelephone and telegraph signals the combination with a pair of sidecircuits, a plurality of terminal telephone circuits, and a plurality oftele raph circuits of a composite set for directing the telephone andtelegraph signals into their respective circuits, said composite setcomprising a coil for associating one of said telegraph circuits witheach line wire of said circuits, and means comprising cores common tosaid coils for producing a change of inductance in all of said coilscorresponding to a change of inductance in any one of them, said coilshaving portions of their windings reversed to neutralize the potentialsgenerated in said coils.

5. In a signaling system adapted for the simultaneous transmission oftelephone andtelegraph signals the combination with a pair of sidecircuits, and terminal telephone and telegraph circuits of a compositeset for directing the telephone and telegraph signals into theirrespective circuits, said composite set comprising a pair of retardationcoils serially bridged across each of said side circuits, said coilshaving windings disposed equally on a plurality of cores such that theflux paths of all of the coils are common, said windings being poled sothat the re- -sultant voltage induced in any of the coils due to avoltage impressed on any of the others is negligible.

6. In a signaling system adapted for the simultaneous transmission oftelephone and telegraph signals the combination with a pair of sidecircuits adapted for phantom operation of terminal telephone andtelegraph circuits, of a composite set for directing the signals intotheir respective channels, said composite set comprising a pair ofretardation coils serially bridged across each of said side circuits,said coils having windings disposed equally on four cores such that theflux paths of all the coils are common, said windings being poled sothat the voltage induced in any of the coils due to a voltage impressedupon any of the others is negligible.

7 In a signaling system adapted for the simultaneous transmission oftelephone and telegraph signals, the combination with a pair of sidecircuits and telephone and telegraph circuits of a composite set fordirecting the telephone and telegraph signals into their respectivecircuits, said composite set comprising a coil having a plurality ofwind v ings :Eor associating one of said telegraph circuits with eachline wire of said side circuits, and means for equalizing the inductanceof all of said coils when any of them are traversed by signal current,said means comprising a winding from each coil upon a core common to allof said coils, said coil windings being poled with respect to each otherso that the resultant voltage induced in any of said coils with saidinductance change is negligible.

In witness whereof, I hereunto subscribe my name this 24th day ofJanuary, 1928. HORACE WHITTLE.

